Since cycloolefin resins produced using cycloolefins as monomers have a bulky alicyclic structure in the main chain skeleton, they are amorphous and have excellent transparency, heat resistance, small coefficient of photoelasticity, and properties of low-water absorption, acid resistance, alkali resistance and high electrical insulation, etc. On this account, uses of cycloolefin polymers for displays (retardation films, diffusion films, liquid crystal substrates, films for touch panels, light guide plates, polarizing plate protective films), optical lenses, optical discs (CD, MD, CD-R, DVD, etc.), optical fibers, optical films/sheets, sealing of photosemiconductors, etc. have been studied.
Of such cycloolefin resins, cycloolefin resins using norbornenes of particularly high reactivity as precursors have been mainly developed, and with remarkable growth of optoelectronics technology, the demand for them has been increased.
As described above, utilization of the films made of the cycloolefin resins as polarizing plate protective films or liquid crystal substrate materials has been expected because the films have relatively small birefringence, and utilization of the films as optical compensation films such as retardation films has been expected because the films have phase difference stability.
For example, in Japanese Patent Laid-Open Publication No. 245202/1992, Japanese Patent Laid-Open Publication No. 36120/1992, Japanese Patent Laid-Open Publication No. 2108/1993 and Japanese Patent Laid-Open Publication No. 64865/1993, phase plates using films of cycloolefin resins are described. In Japanese Patent Laid-Open Publication No. 212828/1993 and Japanese Patent Laid-Open Publication No. 77608/1995, uses of films of cycloolefin resins as protective films for polarizing plates are described. In Japanese Patent Laid-Open Publication No. 61026/1993, a substrate for a liquid crystal display element comprising a film of a cycloolefin resin is described.
On the other hand, liquid crystal displays, practical use of which started with electronic calculators, digital clocks, audio displays, etc., came to be applied to various equipments, such as various mobile equipments (notebook PC, PDA, cellular phones), liquid crystal television sets, car navigation systems and various liquid crystal monitors, making the best use of their features of extremely small thickness, compact size and low power consumption. In the mobile equipments, further, functions of e-mailing and access to information sites are regarded as important because of recent acceleration of the information-oriented age, and for the displays, coloration or much higher precision are desired. Under such circumstances, special characteristics such as capability of being freely controlled in the optical properties have been required for the materials used.
For example, in order to attain high functions and low power consumption, a semi-transmission type display system imparted with a reflection function and a transmission function has been paid attention in the mobile liquid crystal cells of recent years. For the semi-transmission type display system, materials having wavelength dispersion (reciprocal wavelength dispersion properties) such that the phase difference becomes greater toward a longer wavelength side (upward to the right) are required to obtain a circularly polarized light in a wide wavelength region. Retardation films, however, are generally imparted with a function to give phase difference (birefringence) to a transmitted light by stretching and orientation, and as the wavelength of a transmitted light becomes longer, the absolute value of phase difference (birefringence) of the transmitted light tends to become smaller. Therefore, it is very difficult to give specific phase difference, e.g., that of 1/4 wavelength, to a transmitted light in the whole visible region (400 to 800 nm), and in case of the conventional cycloolefin resins, it has not been attained so far to allow one film to exhibit such optical properties of high level.
At present, however, retardation films that give phase difference of 1/4 wavelength in the whole visible region (400 to 800 nm) are actually required for the reflection type or semi-transmission type liquid crystal displays or the pickups for optical discs, and moreover, for the liquid crystal projectors, phase difference of 1/2λ is required.
In case of optical films made of the conventional cycloolefin resins, therefore, two or more films need to be laminated to attain such phase differences. In the production of optical films constituted of laminated films, however, there is a problem that a complicated process including laminating, cutting and bonding of films must be carried out because the two films need to be laminated at precise angles, and hence, productivity becomes extremely bad. Further, there is another problem that the resulting retardation film becomes thick, and this hinders weight lightening or downsizing when they are applied to mobile equipments.
Under the circumstances where downsizing and weight lightening of mobile equipments are promoted as described above, actualization of single-layer optical films having desired phase difference in a wide wavelength region is desired, and development of cycloolefin resins capable of being freely controlled in the magnitude of birefringence and the wavelength dispersion properties according to the properties required in the optical field is eagerly desired.
In the light of such circumstances as mentioned above, the present inventor have earnestly studied, and as a result, they have found that a novel norbornene ring-opened (co)polymer obtained from a specific novel norbornene derivative and a hydrogenation product of the ring-opened (co)polymer can be controlled not only in the magnitude of birefringence (phase difference) but also in the wavelength dependence by designing polymerization composition and substituents of a monomer. Based on the finding, the present invention has been accomplished.
It is an object of the present invention to provide a novel norbornene derivative that is employable as a precursor of a cycloolefin polymer exhibiting excellent transparency, heat resistance and low-water absorption properties and having birefringence and wavelength dispersion properties having been controlled to a desired extent.
It is another object of the present invention to provide a novel norbornene ring-opened (co)polymer capable of producing optical materials having desired birefringence properties and wavelength dependence and having excellent transparency and heat resistance, and a process for preparing the ring-opened (co)polymer.